Final answer:
Group 1A metals form cations with a +1 charge, and group 2A metals form cations with a +2 charge, corresponding to the number of valence electrons they possess.
Step-by-step explanation:
We can predict the charge on group 1A and 2A metals using the periodic table. Metals in group 1A, also known as alkali metals, have one valence electron and thus tend to lose one electron to form cations with a +1 charge. Similarly, metals in group 2A, or alkaline earth metals, have two valence electrons and typically lose both to form cations with a +2 charge.
This corresponds with the periodic table's tendency for main-group elements to form cations with a charge equal to the group number. For example, a sodium atom from group 1A will lose one electron to form a sodium ion (Na+), while a calcium atom from group 2A will lose two electrons to become a calcium ion (Ca2+). This predictable ion formation is particularly applicable to main-group metals, as transition metals can have variable charges.